首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   51046篇
  免费   563篇
  国内免费   427篇
安全科学   1650篇
废物处理   2196篇
环保管理   6980篇
综合类   7948篇
基础理论   13985篇
环境理论   28篇
污染及防治   12759篇
评价与监测   3279篇
社会与环境   2866篇
灾害及防治   345篇
  2022年   406篇
  2021年   444篇
  2020年   305篇
  2019年   404篇
  2018年   737篇
  2017年   745篇
  2016年   1105篇
  2015年   882篇
  2014年   1314篇
  2013年   4030篇
  2012年   1606篇
  2011年   2198篇
  2010年   1817篇
  2009年   1884篇
  2008年   2238篇
  2007年   2247篇
  2006年   2054篇
  2005年   1764篇
  2004年   1735篇
  2003年   1619篇
  2002年   1594篇
  2001年   1951篇
  2000年   1376篇
  1999年   872篇
  1998年   690篇
  1997年   680篇
  1996年   728篇
  1995年   798篇
  1994年   694篇
  1993年   637篇
  1992年   655篇
  1991年   628篇
  1990年   593篇
  1989年   634篇
  1988年   544篇
  1987年   467篇
  1986年   451篇
  1985年   464篇
  1984年   486篇
  1983年   505篇
  1982年   526篇
  1981年   432篇
  1980年   369篇
  1979年   410篇
  1978年   343篇
  1977年   290篇
  1976年   285篇
  1975年   292篇
  1973年   301篇
  1972年   301篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
661.
Egyptian Blue, a multicomponent synthetic blue pigment has been recorded in ancient Egypt since the Fourth Dynasty of the Old Kingdom (2600–2480 B.C.). The pigment consisting of cuprorivaite (CaCuSi4O10) with variable amounts of wollastonite (CaSiO3), Cu-rich glass and cuprite (Cu3O) or tenorite (CuO) was prepared by melting the copper-rich ingredient with lime and desert sand. Low melting temperatures (below 742 °C) were achieved by addition of flux-like plant ashes. The high quality of the pigments collected from monuments of the Fifth Dynasty (2480–2320 B.C.) may indicate that the first manufacture was in early dynastic or perhaps predynastic eras. During the reign of Thutmosis III (18th Dynasty, 1490–1436 B.C.) probably bronze filings were first applied as starting material, thus indicating a technological innovation. This new method was employed till the Roman times.  相似文献   
662.
Hurler's disease was excluded in a fetus at 23 weeks' gestation by demonstrating normal iduronidase activity in fetal leucocytes following failure of amniotic cell culture after amnic-centesis at 16 and 19 weeks' gestation. The diagnosis was confirmed in the neonate.  相似文献   
663.
664.
665.
666.
667.
668.
669.
The long time scale of the climate change problem and the inherent nature of the carbon cycle bring important implications for present technology development efforts. Even if major technology improvements are achieved for non-carbon-emitting technologies such as energy-intensity improvements, wind, solar, biomass, and nuclear over the course of the 21st century, most examinations of potential future greenhouse emissions conclude that additional technology development will be required to stabilize greenhouse gas concentrations. The evelopment of an expanded suite of technologies including carbon capture and disposal, hydrogen systems and biotechnology hold the potential to dramatically reduce the cost of stabilizing greenhouse gas concentrations. This paper examines these technologies in the context of a global integrated assessment model of energy, agriculture, land-use, economics, and carbon cycle processes.  相似文献   
670.
We present a technique to aspirate amniotic fluid from both sacs in biamniotic twin pregnancies using a single abdominal insertion with a spinal needle. It was successful in 48 out of 55 cases of biamniotic twin pregnancies referred to our perinatal unit between 1985 and 1994. The single insertion technique was used when the inter-amniotic membrane was clearly evident and two separate free amniotic fluid pools could be reached by the operator with a single puncture. An adequate amount of amniotic fluid was sampled from both sacs to make a cytogenetic diagnosis in all cases. There were four fetuses with trisomy 21 in three twin pregnancies. In two cases, only one twin was affected whilst the co-twin was normal, so that a selective feticide was performed. No miscarriages due to genetic amniocentesis were reported. After 1990, all genetic amniocenteses in biamniotic twin pregnancies (except for one case due to late booking) were performed between 14 and 15 weeks of gestation and with all cases except one, it was possible to sample both twins by a single puncture. We suggest that early amniocentesis (14–15 weeks) by a single abdominal puncture could be a reliable and safe alternative to first-trimester chorionic villus sampling in twin pregnancies.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号